Field devices are technical systems applied in automation technology and have a direct relationship with a production process. The term “field” refers in automation technology and in process automation to the area outside of circuit cabinets, respectively control stations. Field devices include, in such case, both actuators (control elements, valves, etc.), sensors (pH, temperature, conductivity, turbidity, etc.) as well as also measurement transmitters.
Modern field devices employ a monitoring of their external voltage supply. This can be implemented in hardware, for instance, by a reset generator, and/or by a voltage monitoring in software. When at the field device a reduction of the external supply voltage is detected, the system is shut down and possibly present energy buffers are disconnected. After decay of the remaining energy in the electronics, the device switches off, respectively drops out, due to the lacking of energy supply.
A fluctuating voltage supply or EMC influences can lead to a voltage loss being recognized, although none is present. As a result thereof, the system either shuts down and executes an immediate restart or the system remains showing the last content of the display unit stand, since the residual energy never drained from the electronics.
The first behavior looks to the user like an intermittent problem with the device, while the latter equals a “frozen” measured value on the display unit, i.e. subsequent changes of the measured value are no longer displayed. The user has, in this case, no diagnostic opportunities for detecting the cause of the malfunction. This malfunctioning is possibly first noticed only after some time, since the user has no reason to think the “frozen” display is a malfunction. While it is true that, in this case, most often no erroneous measurement data is transmitted to a, in given cases, present control station, nevertheless an error on the display unit cannot be detected.